Due to their system design, helicopters suffer from high levels of vibration, which are caused by rotation of the rotor blades. For the reasons of construction strength and to reduce the stress on material and the crew, certain limit values for the 1/Rev vibration (aerodynamic imbalance). For this purpose, tracking flights are executed with a measuring system to calculate the actual condition. The required adjustment of the control rod is hereby determined between the swash plate and the respective rotor blade to minimize the imbalance. The helicopter needs to land each time the control rods are adjusted because this adjustment can only be executed the rotor is stationary. After each adjustment, the condition is checked during another flight, wherein the procedure needs to be repeated until the required limit values are met. This procedure is called Rotor Track & Balance (RT&B).
Since however the aerodynamic imbalances are flight condition dependent, the method itself, even after a successful completion of the RT&B procedure, is just a compromise. This can be eliminated by continuous adjustment of the control rods during the flight (In-Flight Tuning). The respective steps and the suitable control rod configurations are for instance known through U.S. Pat. No. 5,511,944; through DE 32 25 571 C2 or DE 10 2009 001 A1, respectively. The last-mentioned German patent application is also considered to be a generic type of the present invention.
The described control rod configuration for adjusting the rotor blades of a helicopter has a control rod with two bearing eyes at the end and an adjustable length range between the bearing eyes. The control rod, at its rotor blade ends, is connected by way of one bearing eye with the rotor blade and at the other end is connected by way of the other bearing eye with the swash plate. The distance between the two bearing eyes can be altered within an adjustment length range by means of a drive positioned in the adjustment length range during the flight. To adjust the length of the control rod, an electromotor and a transmission are provided as the drive in the adjustment area. The integration of the additional parts into the control rod is complex, susceptible to failure, and costly. The integration further increases the weight of the rotor blades that are rotating with control rods.